1. Field of the Invention
The present invention relates generally to a textile dyeing method and apparatus. In particular, the invention relates to a modified dyeing method and apparatus comprising an automated analysis system for a dyebath.
2. Description of Prior Art
The textile industry is a major consumer of water. Approximately 160 pounds of water are required to produce one pound of textile product. Most of the 100 billion gallons of water used by the textile industry each year are consumed primarily in the dyeing and finishing processes for the textiles, namely yarn, fabric and carpet. The vast majority of this water is discharged to the sewer. The waste water, or dyebath, includes dissolved and suspended organic and inorganic chemicals, and, thus, the conventional dyeing process places a significant demand on water resources as well as waste treatment facilities, especially in areas such as Dalton, Georgia, where carpet manufacturing plants are highly concentrated.
In a batch dyeing process, one piece (or several pieces) of the textile product is dyed in a vessel containing the dyebath. The bath is agitated or stirred and/or the textile product is tumbled in the bath so that the single dyebath has repeated contact with each portion of the textile product. The vessel may be pressurized, and heat is added to the bath to provide the desired temperature/pressure/time cycle for the dyeing. The piece of textile is then rinsed and removed from the vessel so that another batch may be dyed, and the depleted dyebath is discarded. The textile material is then dried and/or processed further on other production equipment.
In a continuous dyeing process, a piece of textile product is passed lengthwise through one or more pieces of machinery constituting a dye line or dye range. Subsequent pieces of product are sewn together to form a continuous chain of material proceeding through the dye range. The textile material may be exposed to multiple baths (typically of higher concentration than in batch dyebaths), rinses, and drying stages along its path, but it encounters each stage in succession and for a limited time in each.
Typically, continuous dye processes provide economies of scale and are attractive for larger production lot sizes in a particular color, whereas batch dye processes provide manufacturing flexibility and economic benefits in the case of small lot sizes. Certain products are also more amenable to either continuous or batch dyeing processes.
The nature of the batch dyeing process for textiles is especially wasteful. In the conventional batch dyeing processes, the dyebath is used only once per dye cycle, then discharged to the sewer. In addition, the valuable auxiliary chemicals mixed in the dyebath are lost with each discharged batch of water, which themselves place significant loads on the waste treatment system.
Both continuous and batch dyeing processes are common for broadloom carpets. Continuous dyeing offers cost advantages and greater ease in obtaining uniform color over a large production lot size. In contrast, batch dyeing is now used predominately for heavy-weight, high-end carpets which cannot be dyed as well with a continuous processes. Batch processes also offer the advantage of production flexibility due to the small lot size.
The conventional batch dyeing of nylon broadloom carpets is typically performed in an atmospheric vessel, or beck. Water, auxiliary chemicals, dyes and the carpet are loaded in the beck, with the carpet sewn in a loop so that it continuously enters and exits the dyebath, providing agitation and bath-to-carpet contact. The bath is slowly heated and then held at a specified, critical dying temperature for a given amount of time. Both the temperature and hold time are product dependent. As the bath is heated, the dyes penetrate the fiber of the carpet and form chemical bonds. The elevated bath temperature is held for a sufficient period of time to permit the dyes to migrate to a uniform distribution over the carpet, producing a level dyeing. A patch check on the carpet is then performed, and if the carpet is properly shaded, the bath and carpet are then diluted with fresh water to bring the carpet to a temperature acceptable for handling. The carpet is then removed, and the bath including virtually all of the auxiliary chemicals and any residual dyes is drained to the sewer. Several disadvantages of this conventional process are that it consumes excessive water, wastes the stored thermal energy in the dyebath, and releases dyes and auxiliary chemicals to the waste stream.
The dye used in the batch dyeing process is typically a mixture of three componentsxe2x80x94yellow, red and bluexe2x80x94with a ratio and total quantity selected to give the designed color for the textile product. The auxiliary chemicals used in the batch dyeing process typically include wetting agents, pH control agents, leveling agents, chelating agents, and others which aid the dyeing process, but are not consumed during the dyeing process like the dyes are consumed.
Generally, by the time the finished color of the carpet is achieved in the conventional batch dyeing process, the dyebath has undergone several changes. The dyebath temperature is about 200xc2x0 F., in contrast to the initial starting, ambient temperature of about 60xc2x0 F. There has been a small amount of dilution to the dyebath due to condensate of the injected steam, the preferred mode of heating. Most but not all of the dye has been transferred from the bath to the carpet fiber, but the auxiliary chemicals are essentially unchanged, and remain in the bath.
This spent dyebath, destined for the sewer in the conventional process, represents a significant investment of energy and chemicals which are available for reuse. Dyebath reuse offers the opportunity to reduce the consumption of water resources, to reduce energy consumption in the dyehouse, to conserve/reuse expensive auxiliary chemicals, and to reduce environmental pollution. There is also the potential for production rate increases due to reduced heatup times required by the present invention.
Presently, only for certain combinations of dyes and fibers, there is the possibility to reuse spent dyebaths in subsequent dyeings. However, for these combinations the amount of residual dye left in the baths is generally sufficient to result in off-shade dyeings of subsequent batches. Therefore, for these combinations, the concentration of residual dye for each of the component dyes must be accurately determined, and the recipe for the next dyeing be adjusted accordingly.
Dyebath reuse with manual intervention has been demonstrated on a limited scale for a wide variety of textile products. Yet the barrier to industry-wide implementation is the human involvement required to implement dyebath reuse. A trained chemist is necessary to collect test samples at the end of every dye cycle. The samples must then be transported to an equipped laboratory and analyzed for dye concentrations, and the corrected recipe calculated. It simply is not practical to have personnel on hand round-the-clock to perform these analyses since it can be difficult to find trained chemists willing to work on all shifts, and the employment costs are prohibitive. Further, the human involvement may also lead to analysis and/or calculation errors. Therefore, a solution to this problem is to automate the dyebath analysis process, which the present invention provides.
Various methods and apparatus are known in the textile industry that attempt to relieve some of the disadvantages of the conventional batch dyeing process. For example, U.S. Pat. No. 3,807,872 to Pronier, entitled xe2x80x9cProcess For Regulating The Concentration Of A Bath Of Dye Or Coloring And Equipment For Implementing This Processxe2x80x9d discloses a method and apparatus to control concentration of a dye in a dyebath linearly over time. As disclosed, the first step is the preparation of the dyebath using all the additives except the dye substances. Then a certain volume of the dyebath is taken to act as a pure reference sample. Selected coloring agents are then added to the dyebath and in this way an initial real bath is obtained for dyeing the article. From this real bath, a certain volume is drawn off to form an initial mixed sample. A theoretical consumption curve is simulated by adding steadily and continuously to the initial mixed sample a certain amount of the pure sample. A continuous and steady flow is extracted from the mixed sample and directed to an analysis vessel. Simultaneously, a steady and continuous flow of liquid from the real bath, to which the article to be dyed is added, is directed to a second analysis vessel. Then through analysis, for example, by colorimetry, the liquids passing through the vessels are analyzed. When a difference is detected between the analysis signal corresponding to the mixed sample and real sample, the equilibrium parameters of the real bath are modified in order to cancel out the difference between the two signals.
Specifically, Pronier describes the desire to regulate the rate of change of dye concentration in a bath while the dyeing progresses. It suggests that the rate be regulated by temperature control with regulation efforts which compare the changing color of the dyebath to the changing color of a reference solution. Pronier changes the color of the reference at a linear rate by dilution.
While Pronier describes a desire to make optical measurements on a continuous sampling basis, it describes reasons that this cannot suitably be achieved. Further, the disclosure of Pronier makes clear that the technique does not involve the absolute measurement of the color of the bath. The present invention""s automated analysis system has the capabilities to make the measurements which Pronier suggests can not be done; it can accurately measure the color spectrum of the bath and, therefore, can compute the concentration of each of the individual component dyes. Further, the present invention measures spent dyebaths for reuse in a completely different application of dyebath analysis than Pronier provides, and one for which Pronier is not suitable.
U.S. Pat. No. 4,152,113 to Walker et al., entitled xe2x80x9cSystem For Dyeing Hosiery Goodsxe2x80x9d discloses a system for batch dyeing hosiery goods where the dyebath is recycled and reused in successive dyeing cycles. The dyebath unabsorbed by the hosiery goods is removed from the dye vat or container and directed to a waste water holding tank. Subsequently, spent rinse and finish waters are transferred from the vat to a waste water holding tank after the various rinse and finish operations. Periodically, the waste fluids are directed to a treatment zone where they are clarified sufficiently for utilization in the bath, rinse and finish operations in subsequent dyeing cycles. A small amount of the dyebath directed from a dye waste tank back to a machine via line for a subsequent dyeing cycle is diverted through a line and analyzed by instrumentation to determine the quantities and colors of the various dyes that must be added to result in a desired dye shade of the hosiery goods.
Walker et al. describes a process to clean up dyeing waste water so that it can later be reused. The Walker et al. process specifically attempts to remove the residual dye from the spent bath during the treatment process. The present invention does not rely on a waste treatment system. Instead, it reuses as much of the water, residual dye, auxiliary chemicals, and energy as possible by adding the necessary makeup chemical and dye quantities to make the bath suitable for the next batch. This approach requires the use of an analysis system to reveal the makeup quantity of dye required, but offers greater reuse benefits and avoids the treatment system capital and operating costs.
U.S. Pat. No. 4,350,494 to Scheidegger et al., entitled xe2x80x9cProcess For The Dyeing Of Textile Material And Apparatus For Carrying Out The Processxe2x80x9d discloses batch dyeing of carpet materials, as well as reconditioning and reuse of the exhausted dyebath. The process is characterized in that during dyeing the pH value is lowered, by the addition of an inorganic acid, by at least one unit of pH value. A liquid circulating system is provided including pH monitoring means and dosing means for automatically adding the necessary make-up chemical agents.
Scheidegger et al. describes a process in which pH adjustments are used in an attempt to get all of the dye to be taken up by the product so that there is no residual dye in the spent bath. In the commercial batch processes for nylon carpet of the present invention, there is a small but significant quantity of residual dye in the spent baths. This amount cannot be ignored in a dyebath reuse process without off-shade dyeing in subsequent batches. The present invention operates successfully even if all of the dye happens to be taken up by the product, but also offers the flexibility of being able to deal with the residual dyes that are more typically encountered.
In view of the prior art it can be seen that there is a need for a modified dyeing process incorporating an automated dyebath analysis system that reuses the conventionally wasted dyebaths. It is to the provision of such a method and apparatus that the present invention is primarily directed.
Briefly described, in an exemplary form, the present invention overcomes the above-mentioned disadvantages by providing a modified batch dyeing method and apparatus having an automated dyebath analysis process. The present invention, which applies hot-start and hot-termination to the conventional dyeing process which uses cool-start and cool-termination, modifies the conventional dyeing process to specifically incorporate reuse of the dyebath.
The present invention modifies the conventional batch dyeing process by, in an exemplary embodiment, providing a holding tank separate from the conventional beck, and connected to the beck by appropriate plumbing, which can be added to the conventional batch dyeing apparatus. Further, the present invention has an automated analysis system to analyze the dyebath in the holding tank to accurately determine concentration levels of dyes in the dyebath.
At the same time that the present modified dyeing process prerinses a first carpet of several carpets to be dyed in the beck, the holding tank is filled with water, and auxiliary chemicals are added to the water in the holding tank. Then the proper concentration of dyes are mixed in the dyebath in the holding tank. When the prerinse bath of the present process is dumped to the drain, the present invention transfers the dyebath from the holding tank to the beck via plumbing lines. Upon transferring the dyebath to the beck, the holding tank is rinsed, and the rinse is flushed to the beck.
At this time the beck is fall of dyebath which includes the proper concentration of dyes and auxiliary chemicals, and the holding tank is empty. The temperature of the first bath is slowly heated while the carpet tumbles in the bath. When the temperature of the dyebath reaches the critical dying hold temperature for the type of carpet, the hold temperature of the dyebath is held for a period longer than the conventional process hold time.
Upon a successful patch check of the carpet, a portion of the dyebath is transferred to the holding tank. At this point, the beck is not empty of bath so as to keep the carpet somewhat buoyant, and the holding tank is only partially full. The beck and carpet is then bathed in a cool rinse of water and the carpet brought to a temperature lower than the critical temperature. A portion of the bath in the beck (including the rinse water) is then transferred to the holding tank. At this point, the holding tank is filled with the proper amount of dyebath to be used in the next cycle, and the remaining bath in the beck is drained to the sewer.
Then a cool water rinse is applied to the carpet in the beck to bring the temperature of the carpet to a safe handling temperature and the rinse water left in the beck. While the first carpet is pulled from the beck, a sample of the dyebath in the holding tank is analyzed, and any required auxiliary chemicals and dyes are added to the dyebath.
A second carpet is then installed in the beck, and prerinsed with the rinse water left in the beck from the first carpet dyeing process. This water is then drained from the beck. Then the heated dyebath in the holding tank, which is at an elevated temperature and composed of the proper concentrations of chemicals and dye, is transferred to the beck and the process is repeated.
Several challenges were overcome in order to make dyebath reuse possible and attractive to the textile industry. Generally, the waste produced by conventional dyeing process challenged the inventors to create a more efficient dyeing process. Reuse of the dyebath was an opportunity to significantly curtail the waste of dyes, auxiliary chemicals, thermal energy, water, and effluent of the conventional batch dyeing process. Yet the process of dyebath reuse presented its own challenges, challenges which are overcome by the present invention.
The first challenge was in the necessary changes to the conventional dyeing process. Conventional dyeing starts cold with gradual heating, and at the end of the cycle, the bath and carpet are cooled by dilution. Yet, for effective capture and reuse of the energy and chemicals, the bath must be recovered hot, without significant dilution, and the subsequent batch must be started hot. Yet if the conventional process were to use hot-start and hot-termination of the dyeing process, it would result in product quality defects, and suitable adjustments would have to be developed and implemented. Therefore, the industry did not attempt this approach.
The second challenge was represented by the small and variable quantity of residual dyes in the spent bath. If these were neglected when a dyebath was reused, subsequent dyeings would be off-shade. It was necessary for the spent bath to be captured, analyzed for the residual quantity of each dye component, and reconstituted to the proper concentration of each dye component as called for in the recipe for the subsequent batch.
In order to be eligible for dyebath reuse, the subsequent batch must use the same auxiliary chemical recipe and the same component dyes as the previous batch, although it may specify a different shade. In most dyehouses, the majority of the products can be dyed with a combination of just three dyes, typically a yellow, a red, and a blue. Some colors may require a different combination, such as a different yellow dye, or an orange dye instead of yellow. Carpets which use different component dyes in their recipes cannot be dyed in the same reuse sequence because of the dye contamination which would result.
The third challenge was the automation of the present invention. Several industrial scale demonstrations of dyebath reuse were conducted in the 1970xe2x80x2s and 1980xe2x80x2s, demonstrating the technical feasibility and economic advantages. The process did not achieve commercial acceptance because of the required human involvement. Even though the savings could justify the added labor, plants were not prepared to accept the additional tasks, the additional technical expertise required, nor the risk that human delays or errors in chemical analyses and calculations could adversely impact the production schedule. Thus, commercial acceptance of dyebath reuse required that the process be automated and not impose significant burdens on the production system.
Thus, the present invention comprises a modified batch dyeing method and apparatus that removes the quality defects associated with conventional attempts at a hot-start, hot-termination dyeing process, an analysis process and apparatus to analyze the spent dyebath that will be reused, and provides the necessary automation of the entire process to make the present invention economically attractive to the textile industry.
Three steps are introduced to the conventional batch dyeing process by the present invention to overcome the various problems associated with the hot-start of the batch dyeing process:
1. The carpet is pre-rinsed in a bath containing a leveling agent so that the entire carpet is xe2x80x9ctreatedxe2x80x9d with the leveling agent before it comes in contact with the dye. This additional pre-rinse step is introduced before the dyeing process begins to remove finishes and tints which are added to the fibers during the carpet""s initial processing.
2. The dyebath is prepared in a separate vessel from where the dyeing is performed so that the dyes can be fully diluted in the bath prior to contact with the carpet. The conventional process adds the dyes directly to the bath in the process vessel which may lead to the problem of spot dyeing.
3. The hold time at the maximum normal process dying temperature (critical dying temperature) is extended to permit migration of the dye from point to point on the carpet to achieve levelness of dyeing. The additional process time added is balanced by the reduction in the time needed to heat the bath since the bath is hot at the beginning of each reuse batch.
Process quality defects associated with the hot-termination of dyeing are also avoided in the present invention. Upon the expiration of the conventional process hold time, and before the final cool rinse of the carpet, the present invention slightly cools the bath below a certain, critical cooling temperature that is only a few degrees below the normal process dying temperature. When the bath temperature is lower than the critical cooling temperature, it is transferred to the holding tank for reuse, and a further cool rinse bath may be introduced into the beck to cool the carpet for safe handling. It has been found that when the bath and carpet are slowly cooled below the critical temperature before transferring the bath to the holding tank, the quality defects of the conventional process do not occur when coupled with hot-termination.
The present invention incorporates an automated system to continuously analyze the spent dyebath to determine the concentration of each component of the residual dyes. The automated analysis system provides the analysis so the bath may be reconstituted to the proper dye concentrations for the next dyeing batch. By automating the analysis process, the adverse human factors previously addressed are eliminated. The automated analysis system is can be interfaced with the plant""s existing process control system and incorporates all of the required chemistry expertise in the analysis system""s hardware and software.
The analysis technique for the automated analysis of the spent dyebath is preferably absorbance spectrophotometry. In one embodiment, a dual flow cell permits a single light source to illuminate both a sample of the dyebath and a sample of a reference solution consisting of water and all of the auxiliary chemicals in the same concentration as in the dyebath (i.e., everything except the dyes). The light passing through the two samples is captured by optical fibers and carried to a dual-beam spectrophotometer which measures the light absorbance for the wavelengths covering the visible spectrum. The absorbance spectrum for the reference sample is subtracted from the spectrum for the dyebath sample, providing the absorbance spectrum of just the residual dyes.
Another embodiment of the analysis system involves a single-beam configuration. This involves measuring both the reference solution and the dyebath sample in the same flow cell at different times. This embodiment involves only one single flow cell, one light source with no beam splitter, and a single beam spectrometer. The measurement of the reference solution may be performed either just prior to, or well in advance of the dyebath sample and stored in an electronic file.
Objectives of the present invention include reduced water consumption, reduced environmental pollution, and energy and chemical conservation through efficient reuse of the dyebaths. The present invention incorporates these objectives which leads to an economically-attractive modified batch dyeing process.
Thus it can be seen that there is a need for a modified batch dyeing process comprising an automated dyebath analysis system that reuses the conventionally wasted dyebaths, and that is capable of a hot-start and hot-termination. It is to the provision of such a method and apparatus that the present invention is primarily directed.